A Patient's Guide to a Low White Blood Cell Count

A Patient's Guide to a Low White Blood Cell Count
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A low white blood cell count is also referred to as leukopenia. It occurs when the patient’s white blood cells, also referred to as leukocytes, decrease. These cells are responsible for helping the body fight disease and infection and they are found in the blood. In adults, these cells are considered low when there are less than 3,500 of them per microliter of blood. In children, it varies and depends on their gender and age.


There are five types of white blood cells: neutrophils, basophils, lymphocytes, eosinophils, and monocytes. These can be divided further into two categories: mononuclear leukocytes and granulocytes.

  • Neutrophils: This type of white blood cell is the most plentiful in the bloodstream. Their job is to use the enzymes within their cytoplasm’s grains to break down bacterial cells inside the body.
  • Eosinophils: The exact function of these cells are unknown. However, their numbers do increase when parasites or allergens are present.
  • Basophils: This cell is the least plentiful in the bloodstream. They are involved in starting the inflammation process. Inflammation is a body process that occurs when the body is responding to irritation or injury. When the inflammation process occurs, basophils migrate to the site of inflammation from the bloodstream.
  • Monocytes: These are the largest of all of the white blood cells and are mononuclear leukocytes. These cells eat microorganisms that should not be present in the body. To do this they surround them and then they digest them. They also assist in the removal of other cellular material from the body that is unneeded and eat and digest old and dead cells.
  • Lymphocytes: These are the second most plentiful white blood cell in the blood stream and are the smallest. They travel throughout the body, using the blood, but they can also travel freely in other tissues and get back to the blood by traveling through the lymphatic channels.


There are main causes and specific causes of a low white blood cell count.

Main Causes

  • Disrupted bone marrow function due to a viral infection.
  • Diminished bone marrow function due to a congenital disorder.
  • Destruction of bone marrow cells or white blood cells due to an autoimmune disease.
  • Severe infections that cause these cells to be used up faster than the body can produce them.
  • Drugs and medications that damage bone marrow or destroy these cells.

Specific Causes

  • Allergies, particularly severe allergic reactions.
  • Vitamin deficiencies.
  • Aplastic anemia.
  • Rheumatoid arthritis.
  • Drugs and medications, such as diuretics, antibiotics, and prednisone.
  • Radiation therapy.
  • Parasitic diseases.
  • Histoplasmosis.
  • Congenital disorders.
  • Hypersplenism.
  • Autoimmune disorders.
  • Hyperthyroidism.
  • Myelokathexis.
  • Infectious diseases.
  • Myelofibrosis.
  • Kostmann’s syndrome.
  • Myelodysplastic syndromes.
  • Leukemia.
  • Lupus.


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Testing a patient’s leukocyte count involves blood testing. To do this, a healthcare professional will use a needle and insert it into the patient’s vein. They will extract the amount of blood ordered by the patient’s doctor. This will then be sent off to a laboratory to be analyzed.

The most common test is a standard blood count, also referred to as a total leukocyte count. It measures how many white blood cells a patient has per microliter of blood. This allows doctors to test a specific type of leukocyte to see if it is lower, or higher, that it should be.

Another test, called a differential count, will measure how many neutrophils, monocytes, basophils, lymphocytes, and eosinophils a patient has per microliter of blood. When healthy, the blood is made up of 60 percent neutrophils, 5 percent monocytes, 1 percent basophils, 30 percent lymphocytes, and 4 percent eosinophils.


Mayo Clinic. (2010). Low White Blood Cell Count. Retrieved on January 17, 2010 from the Mayo Clinic: https://www.mayoclinic.com/health/low-white-blood-cell-count/MY00162